The others have the benefits of being in countries outside of the original five areas of FFXIV (Ishgard, Ul'dah, Gridania, Limsa Lominsa, and Mor Dhona). Of the ones who show up in the original, you have Moogles, Ixali, Sylphs, Amal'jaa, Sahagin, Kobolds, and Dravanians (I add the last as a meaningful one as they're the catalyst for Shiva to an extent). Only three of those don't pop up, and two of them are dependent on things unique to the Source, so Sylphs are just the odd man out. Not saying that them being killed in the Flood isn't the case, it just seems like a strange omission when the others all showed up. Would have been neat to see them with the Pixies and perhaps compare/contrast the two.